Coil unit and wireless power transmission device

ABSTRACT

A coil unit includes a non-magnetic conductive plate which is disposed along an axis of a coil, and a magnetic body. The magnetic body includes a first portion which is positioned in an outer side than an outline of one side of the conductive plate in the axis direction of the coil, and a second portion which is positioned in an outer side than an outline of the other side of the conductive plate in the axis direction of the coil. When viewing from the axis direction of the coil, the first and second portions are positioned on a side of the conductive plate where is opposite to a side which faces the coil.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a coil unit and a wireless powertransmission device.

2. Description of the Related Art

Recently, in order to transmit power without mechanical contact by acable or the like, a wireless power transmission technique usingelectromagnetic induction operation between a primary (transmission)coil and a secondary (power receiving) coil which face each other hasattracted attention, and is expected to be widely used as a powerfeeding device for charging a secondary battery mounted in an electricvehicle (EV) or a plug-in hybrid electric vehicle (PHEV).

In a case in which a wireless power transmission technique is applied toa power feeding device for an electric vehicle or the like, it isassumed that a positional relationship between a transmission coilprovided on the ground and a power receiving coil mounted in an electricvehicle or the like is not necessarily constant. In this way, in a casein which the positions of the transmission coil and the power receivingcoil are shifted, magnetic coupling between the coils is significantlyreduced, and as a result, there is a problem in which power transmissionefficiency is reduced.

In Japanese Unexamined Patent Application Publication No. 2010-172084, atechnique of a non-contact power feeding device using a plurality ofcores disposed at predetermined intervals on a flat surface has beenproposed. Japanese Unexamined Patent Application Publication No.2010-172084 discloses that the non-contact power feeding device isresistant to a positional shift since the plurality of cores operate ascores with sizes expanded by including a gap therebetween.

In the technique disclosed in Japanese Unexamined Patent ApplicationPublication No. 2010-172084, the plurality of cores are disposed atpredetermined intervals on a flat surface, each core using a coil inwhich a winding wire is wound in a helical shape, and thus powertransmission efficiency can be increased. However, in a case of the coilin which a winding wire is wound in a helical shape into the cores,since a magnetic flux which is circulated up to a place separated fromthe coil is easily generated, there is a problem that an unnecessaryleakage magnetic field is easy to be formed in the place separated fromthe coil. Particularly, in a case in which a wireless power transmissiontechnique is applied to a charging device for a power electronic devicesuch as an electric vehicle, since it is necessary to make a largecurrent flow through the coil because a large power transmission isrequired, there is a possibility that a leakage magnetic field strengthformed in the place separated from the coil may also increase, andelectromagnetic interference negatively affecting a peripheralelectronic apparatus or the like may occur.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a coilunit and a wireless power transmission device in which a decrease ofpower transmission efficiency is suppressed and an unnecessary leakagemagnetic field formed in a place separated from the coil unit isreduced.

A coil unit according to the present invention, which wirelesslytransmits a power from a transmission side to a power receiving side,includes: a coil on which a winding wire is wound in a helical shape; anon-magnetic conductive plate which is disposed along an axis of thecoil; and a magnetic body. The magnetic body includes a first portionwhich is positioned in an outer side than an outline of one side of theconductive plate in an axis direction of the coil, and a second portionwhich is positioned in an outer side than an outline of the other sideof the conductive plate in the axis direction of the coil. When viewingfrom the axis direction of the coil, the first and second portions arepositioned on a side of the conductive plate where is opposite to a sidewhich faces the coil.

According to the present invention, since the magnetic body includes thefirst portion which is positioned in the outer side than the outline ofone side of the conductive plate in the axis direction of the coil, andthe second portion which is positioned in the outer side than theoutline of the other side of the conductive plate in the axis directionof the coil, a magnetic path with a low magnetoresistance is formed.That is, a magnetoresistance of a magnetic path which passes through themagnetic body is smaller than a magnetoresistance of a magnetic pathwhich is widely circulated up to a place separated from the coil unit.Thus, the magnetic flux easily forms the magnetic path which passesthrough the magnetic body, and the magnetic flux hardly forms themagnetic path which is circulated up to a place separated from the coilunit. As a result, since magnetic flux density of a place separated fromthe coil unit is decreased, a strength of an unnecessary leakagemagnetic field which is formed in a place separated from the coil unitis decreased. Furthermore, since magnetic coupling of the coil and themagnetic body is prevented from excessively increasing by thenon-magnetic conductive plate which is disposed in the axis direction ofthe coil, magnetic coupling of a transmission side and a power receivingside in the wireless power transmission can be prevented fromsignificantly decreasing. As a result, a decrease of power transmissionefficiency is suppressed.

It is preferable that the magnetic body further include a third portionwhich is positioned between the first portion and the second portion,and imaginary component values of permeability of the first and secondportions be smaller than an imaginary component value of permeability ofthe third portion. That is, since the first and second portions of themagnetic body have small imaginary component values of permeability,loss and heat generation in the first and second portions are small,even in a case in which magnetic flux density of the first and secondportions is high. Thus, even if a position of the coil unit is shiftedand the magnetic flux density of the first or second portion which ispositioned in an outer side than an outline of the conductive plate islocally increased, the loss and heat generation in the first and secondportions can be reduced.

A wireless power transmission device according to the present invention,which wirelessly transmits by a transmission coil and a power receivingcoil unit facing each other, includes: the transmission coil in which awinding wire is wound on a magnetic core; and the power receiving coilunit which is configured with the above-described coil unit. Whenviewing from a facing direction of the transmission coil and the powerreceiving coil unit, an outline of a conductive plate of the powerreceiving coil unit is positioned in an outer side than an outline ofthe magnetic core.

According to the present invention, magnetic coupling of thetransmission coil and the magnetic body is more effectively preventedfrom excessively increasing by the conductive plate, and among themagnetic fluxes which are generated by the transmission coils, themagnetic flux which is not interlinked with the power receiving coilselectively forms a magnetic path which passes through the magneticbody. As a result, a decrease of power transmission efficiency issuppressed, and an effect in which a leakage magnetic field is reducedis increased even more.

A wireless power transmission device according to the present invention,which wirelessly transmits by first and second transmission coils and apower receiving coil unit facing each other, includes: the first andsecond transmission coils in which directions of magnetic fieldsgenerated when a current flows are reversed to each other, and areapposed; a magnetic core which is disposed along an arrangementdirection of the first and second transmission coils; and the powerreceiving coil unit which is configured with the above-described coilunit. When viewing from a facing direction of the first and secondtransmission coils and the power receiving coil unit, an outline of theconductive plate of the power receiving coil unit is positioned in anouter side than an outline of the magnetic core of the the first andsecond transmission coils.

According to the present invention, magnetic coupling of the first andsecond transmission coils and the magnetic body is more effectivelyprevented from excessively increasing by the conductive plate, and amongthe magnetic fluxes which are generated by the first and secondtransmission coils, the magnetic flux which is not interlinked with thepower receiving coil selectively forms a magnetic path which passesthrough the magnetic body. As a result, a decrease of power transmissionefficiency is suppressed, and an effect in which a leakage magneticfield is reduced is increased even more.

A wireless power transmission device according to the present invention,which wirelessly transmits by a transmission coil unit and a powerreceiving coil facing each other, includes: the transmission coil unitwhich is configured with the above-described coil unit; and the powerreceiving coil. The coil of the transmission coil unit includes amagnetic core. When viewing from a facing direction of the transmissioncoil unit and the power receiving coil, an outline of the conductiveplate of the transmission coil unit is positioned in an outer side thanan outline of the magnetic core.

According to the present invention, magnetic coupling of the coilsincluded in the transmission coil unit and the magnetic body is moreeffectively prevented from excessively increasing by the conductiveplate, and among the magnetic fluxes which are generated by the coilsincluded in the transmission coil unit, the magnetic flux which is notinterlinked with the power receiving coil selectively forms a magneticpath which passes through the magnetic body. As a result, a decrease ofpower transmission efficiency is suppressed, and an effect in which aleakage magnetic field is reduced is increased even more.

As described above, according to the present invention, it is possibleto provide a coil unit which suppresses a decrease of power transmissionefficiency, and can reduce an unnecessary leakage magnetic field whichis formed in a place separated from the coil unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system configuration diagram illustrating, with a load, awireless power transmission device according to a first embodiment ofthe present invention.

FIG. 2 is a schematic cross-sectional diagram illustrating atransmission coil and a power receiving coil unit of the wireless powertransmission device according to the first embodiment of the presentinvention.

FIG. 3 is a diagram schematically illustrating a magnetic flux which isgenerated by first and second transmission coils, in a cross-sectionaldiagram illustrating a power receiving coil unit according to a secondembodiment of the present invention, the first and second transmissioncoils, and magnetic cores of the first and second transmission coil.

FIG. 4 is a diagram schematically illustrating a magnetic flux which isgenerated by a transmission coil, in a cross-sectional diagramillustrating a transmission coil unit according to a third embodiment ofthe present invention, and a power receiving coil.

FIG. 5 is a diagram schematically illustrating a magnetic flux which isgenerated by a transmission coil, in a cross-sectional diagramillustrating a power receiving coil unit according to a fourthembodiment of the present invention, and the transmission coil unit.

FIG. 6 is a diagram schematically illustrating a magnetic flux which isgenerated by the transmission coil, in a case in which a positionalshift occurs in the power receiving coil unit and the transmission coilin FIG. 5.

FIG. 7 is a cross-sectional diagram of a power receiving coil and atransmission coil of a comparative example.

FIG. 8 is a measurement result of a leakage magnetic field strength andpower transmission efficiency of first and second examples and acomparative example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments for executing the present invention will be described indetail with reference to the drawings. In the description, the samesymbols or reference numerals will be attached to the same elements orthe elements having the same functions, and repeated description will beomitted.

First Embodiment

An entire configuration of a wireless power transmission device S1according to a first embodiment of the present invention will be firstdescribed with reference to FIG. 1 and FIG. 2. In the presentembodiment, an example in which a coil unit according to the presentinvention is applied to a power receiving coil unit of the wirelesspower transmission device is described. FIG. 1 is a system configurationdiagram illustrating the wireless power transmission device according tothe first embodiment of the present invention, and a load. FIG. 2 is aschematic cross-sectional diagram illustrating a transmission coil and apower receiving coil unit, according to the first embodiment of thepresent invention. FIG. 2 schematically illustrates magnetic fluxeswhich are generated by a transmission coil Lt. In FIG. 2, magneticfluxes in the inside of magnetic cores Ct and Cr of a transmission coilLt and a power receiving coil Lr, and a magnetic flux in the inside ofmagnetic body Fa are not illustrated. In addition, in FIG. 2, asrepresentations of the magnetic fluxes which are generated by thetransmission coil Lt, a magnetic flux Bt1 which is interlinked with apower receiving coil Lr, a magnetic flux Bn1 which is widely circulatedup to a place separated from the power receiving coil unit Lru1, and amagnetic flux Bf1 which passes through the magnetic body Fa areillustrated.

As illustrated in FIG. 1, the wireless power transmission device S1includes a wireless transmission device Ut1 and a wireless powerreceiving device Ur1.

The wireless transmission device Ut1 includes a power supply PW, aninverter INV, and the transmission coil Lt. The wireless power receivingdevice Ur1 includes the power receiving coil unit Lru1 and arectification circuit DB.

The wireless transmission device Ut1 will be first described. The powersupply PW supplies the inverter INV which will be described later withDC power. As the power supply PW, all kinds of devices which output DCpower can be used, and a DC power supply which rectifies commercial ACpower and smoothes the rectified power, a secondary battery, a DC powersupply which generates power from light, a switching power supply devicesuch as a switching converter, or the like can be used.

The inverter INV has a function of converting an input DC power which issupplied from the power supply PW into AC power. In the presentembodiment, the inverter INV converts the input DC power which issupplied from the power supply PW into AC power and supplies thetransmission coil Lt which will be described later with the AC power.The inverter INV is configured by a switching circuit in which aplurality of switching elements are bridge-connected. As the switchingelement which configures the switching circuit, an element, such as, ametal oxide semiconductor field effect transistor (MOSFET), or aninsulated gate bipolar transistor (IGBT) can be used.

As described in FIG. 2, the transmission coil Lt includes the magneticcore Ct and a winding wire Wt. The transmission coil Lt is a solenoidcoil on which a winding wire is wound in a helical shape, and is formedby winding the winding wire Wt which is configured by a litz wire, suchas, copper or aluminum on the magnetic core Ct in a plate shape or in arod shape. An axis direction of the transmission coil Lt is orthogonalto a facing direction of the transmission coil Lt and the powerreceiving coil unit Lru1 which will be described later. The number ofturns of the transmission coil Lt is approximately set based on apredetermined distance between the power receiving coil Lr which will bedescribed later and the transmission coil, a desired power transmissionefficiency, or the like. In a case in which the wireless powertransmission device S1 according to the present embodiment is applied toa power feeding facility for a vehicle such as an electric vehicle, thetransmission coil Lt is disposed in the ground or on a portion near theground.

Next, a configuration of the wireless power receiving device Ur1 will bedescribed. The power receiving coil unit Lru1 has a function ofreceiving AC power which is transmitted from a transmission coil Lt. Ina case in which the wireless power transmission device S1 according tothe present embodiment is applied to a power feeding facility to avehicle such as an electric vehicle, the power receiving coil unit Lru1is mounted on a lower portion of the vehicle. The power receiving coilunit Lru1 includes the power receiving coil Lr, a conductive plate Sa,and the magnetic body Fa.

As described in FIG. 2, the power receiving coil Lr includes themagnetic core Cr and a winding wire Wr. The power receiving coil Lr is asolenoid coil on which a winding wire is wound in a helical shape, andis formed by winding the winding wire Wr which is configured by a litzwire, such as, copper or aluminum on the magnetic core Cr in a plateshape or in a rod shape. An axis direction of the power receiving coilLr is orthogonal to a facing direction of the transmission coil Lt andthe power receiving coil unit Lru1. The number of turns of the powerreceiving coil Lr is approximately set based on a predetermined distancebetween the transmission coil Lt and the power receiving coil, a desiredpower transmission efficiency, or the like.

The conductive plate Sa is disposed along an axis of the power receivingcoil Lr. Specifically, the conductive plate Sa is disposed along asurface of the power receiving coil Lr opposite to a surface which facesthe transmission coil Lt, and is disposed parallel to the axis of thepower receiving coil Lr. The conductive plate Sa functions as a magneticshield material for preventing magnetic coupling of the transmissioncoil Lt or the power receiving coil Lr, and the magnetic body Fa whichwill be described later from being excessively increased. Specifically,the conductive plate Sa functions as a shield material which reducespassage of a magnetic flux by cancelling a magnetic field using aninduced current, an eddy current, or the like. Thus, as a conductiveplate Sa, all kinds of non-magnetic conductors, the surfaces of whichfunction as electromagnetic shield materials can be used, and aluminum,copper, a steel plate, the surface of which is plated by zinc, or thelike can be used. In the present embodiment, in a case in which a centerpoint of the transmission coil Lt overlaps a center point of the powerreceiving coil unit Lru1 when viewing from a facing direction of thetransmission coil Lt and the power receiving coil unit Lru1, an outlineof the conductive plate Sa of the power receiving coil unit Lru1 ispositioned in an outer side than the outline of the magnetic core Ct ofthe transmission coil Lt. For this reason, the magnetic coupling of thetransmission coil Lt and the magnetic body Fa which will be describedlater can be effectively prevented from excessively increasing by theconductive plate Sa. Also, among the magnetic fluxes which are generatedby the transmission coil Lt, the magnetic flux which is not interlinkedwith the power receiving coil Lr selectively forms a magnetic path whichpasses though the magnetic body Fa which will be described. As a result,a decrease of power transmission efficiency is suppressed, and an effectin which a leakage magnetic field is reduced is increased even more.

The magnetic body Fa is disposed along a surface of the conductive plateSa opposite to a surface which faces the power receiving coil Lr. Inaddition, since forming a magnetic circuit with a low magnetoresistance,the magnetic body Fa is formed by a material with a high relativepermeability. Specifically, if the relative permeability of the magneticbody Fa is greater than 1, a magnetoresistance ratio of the magneticbody Fa is lower than that of a surrounding space, and thus when themagnetic body Fa forms a magnetic circuit with a low magnetoresistance,an effect in which a leakage magnetic field is reduced is obtained. Inthe present embodiment, In order to more effectively decrease theleakage magnSetic field, the magnetic body Fa is configured by amaterial with a relatively high relative permeability such as steel or aferrite. In the present embodiment, the magnetic body Fa is configuredby one plate, but the present invention is not limited to this. Forexample, multiple plates may be disposed so as to be separated from eachother. In all cases, a magnetic circuit with a high magnetoresistancecan be formed by the magnetic body Fa. Furthermore, the magnetic body Famay be used instead of a vehicle configuration components positioningnear a lower portion of a vehicle, which are configured by a magneticbody.

In addition, the magnetic body Fa includes a first portion F1A which ispositioned in an outer side than the outline of one side of theconductive plate Sa in an axis direction of the power receiving coil Lr,and is positioned on a side of the conductive plate Sa opposite to aside which faces the power receiving coil Lr, when viewing from the axisdirection of the power receiving coil Lr. That is, the magnetic body Faprotrudes toward an outer side (left side in the figure) than an outline(left end in the figure) of one side of the conductive plate Sa in theaxis direction of the power receiving coil Lr.

In addition, furthermore, the magnetic body Fa includes a second portionF2A which is positioned in an outer side than the outline of the otherside of the conductive plate Sa in an axis direction of the powerreceiving coil Lr, and is positioned on a side of the conductive plateSa opposite to a side which faces the power receiving coil Lr, whenviewing from the axis direction of the power receiving coil Lr. That is,the magnetic body Fa protrudes toward an outer side (right side in thefigure) than an outline (right end in the figure) of the other side ofthe conductive plate Sa in the axis direction of the power receivingcoil Lr. The magnetic body Fa may or may not protrude toward an outerside than the outline of the conductive plate Sa, in a directionorthogonal to the axis direction of the power receiving coil Lr. In thepresent embodiment, a length of the conductive plate Sa and a length ofthe magnetic body Fa are approximately the same, in a directionorthogonal to the axis direction of the power receiving coil Lr.

The rectification circuit DB has a function of rectifying AC power thatthe power receiving coil Lr receive into DC power. As the rectificationcircuit DB, a conversion circuit which includes a full-waverectification function using a diode bridges, and a power smoothingfunction using a capacitor and a three-terminal regulator, or the likeis used. DC power which is rectified by the rectification circuit DB isoutput to a load R. Here, in a case in which the wireless powertransmission device S1 according to the present embodiment is applied toa power feeding facility to a vehicle such as an electric vehicle, asecondary battery mounted in the vehicle is used as the load R.

Next, a magnetic flux which is generated by the transmission coil Ltaccording to the present embodiment, and a reduction effect of anunnecessary leakage magnetic field will be described in detail withreference to FIG. 2.

As illustrated in FIG. 2, the transmission coil Lt generates themagnetic flux Bt1 which is interlinked with the power receiving coil Lr.Since the magnetic flux Bt1 is interlinked with the power receiving coilLr, an electromotive force is generated in a winding wire Wr of thepower receiving coil Lr. Then, the power which is generated in the powerreceiving coil Lr is rectified by the rectification circuit DB, and isoutput to the load R. Here, since the conductive plate Sa is disposedalong a surface on a side of the power receiving coil Lr opposite to asurface which faces the transmission coil Lt, the magnetic flux Bt1forms a magnetic path which passes through the magnetic body Fa, andthereby a decrease of the magnetic flux which is interlinked with thepower receiving coil Lr is suppressed. That is, by the conductive plateSa, magnetic coupling of the transmission coil Lt or the power receivingcoil Lr, and the magnetic body Fa can be prevented from excessivelyincreasing, and magnetic coupling of the transmission coil Lt and thepower receiving coil Lr can be prevented from significantly decreasing.As a result, a decrease of power transmission efficiency is suppressed.Particularly, in the present embodiment, when viewing from a facingdirection of the transmission coil Lt and the power receiving coil Lr,the outline of the conductive plate Sa is positioned in an outer sidethan the outline of the magnetic core Ct of the transmission coil Lt.Thus, by forming a magnetic path such that the magnetic flux Bt1 passesthrough the magnetic body Fa, a decrease of a magnetic flux which isinterlinked with the power receiving coil Lr can be effectivelysuppressed. That is, by the conductive plate Sa, the magnetic couplingof the transmission coil Lt and the magnetic body Fa is prevented fromexcessively increasing.

Meanwhile, as illustrated in FIG. 2, the transmission coil Lt generatesthe magnetic flux Bnl which is not interlinked with the power receivingcoil Lr, and is widely circulated up to a place separated from the powerreceiving coil unit Lru1. The magnetic flux Bn1 which is widelycirculated up to a place separated from the power receiving coil unitLru1 forms an unnecessary leakage magnetic field in a place separatedfrom the power receiving coil unit Lru1. In addition, the transmissioncoil Lt generates the magnetic flux Bf1 which is not interlinked withthe power receiving coil Lr, and passes through the magnetic body Fa.Since circulating the periphery of the power receiving coil unit Lru1,the magnetic flux Bf1 which passes through the magnetic body Fa does notform a magnetic path which is circulated up to place separated from thepower receiving coil unit Lru1.

Here, since a magnetoresistance ratio of the magnetic body Fa is lowerthan a magnetoresistance ratio of a surrounding space, amagnetoresistance of a magnetic path which passes through the magneticbody Fa is smaller than a magnetoresistance of a magnetic path which iswidely circulated up to a place separated from the power receiving coilunit Lru1. Thus, the magnetic flux Bf1 which passes through the magneticbody Fa increases, and the magnetic flux Bn1 which is circulated up to aplace separated from the power receiving coil unit Lru1 decreases. As aresult, since the magnetic flux Bn1 which is widely circulated up to aplace separated from the power receiving coil unit Lru1 decreases,magnetic flux density of a place separated from the power receiving coilunit Lru1 is decreased, and a strength of an unnecessary leakagemagnetic field represented by a magnetic flux density of a placeseparated from the power receiving coil unit Lru1 is also decreased.

In addition, the first and second portions F1A and F2A of the magneticbody Fa are disposed so as to be positioned on the outside of both endsin an axis direction of the power receiving coil Lr of the conductiveplate Sa, and thus, among the magnetic fluxes which are generated by thetransmission coil Lt, the magnetic flux which is not interlinked withthe power receiving coil Lr, more easily forms a magnetic path whichpasses through the magnetic body Fa. That is, the first and secondportions F1A and F2A are disposed such that a magnetoresistance of themagnetic path formed by the magnetic body Fa is smaller. Thus, anunnecessary leakage magnetic field can be effectively reduced.

Furthermore, in the present embodiment, when viewing from a facingdirection of the transmission coil Lt and the power receiving coil Lr,the outline of the conductive plate Sa is positioned in an outer sidethan the outline of the magnetic core Ct of the transmission coil Lt.Thus, it is possible to effectively prevent the magnetic flux Bt1 whichis interlinked with the power receiving coil Lr from forming a magneticpath which passes through the magnetic body Fa, and a magnetic fluxwhich is not interlinked with the power receiving coil Lr selectivelyforms a magnetic path which passes through the magnetic body Fa. As aresult, a decrease of power transmission efficiency is suppressed, andan effect in which a leakage magnetic field is reduced is increased evenmore.

-   -   As described above, in the power receiving coil unit Lru1        according to the present embodiment, the magnetic body Fa        includes the first portion F1A which is positioned in an outer        side than the outline of one side of the conductive plate Sa in        an axis direction of the power receiving coil Lr, and the second        portion F2A which is positioned in an outer side than the        outline of the other side of the conductive plate Sa in an axis        direction of the power receiving coil Lr, and thereby a magnetic        path with a low magnetoresistance is formed. That is, since the        magnetoresistance of the magnetic path which passes through the        magnetic body Fa is smaller than the magnetoresistance of the        magnetic path which is widely circulated up to a place separated        from the power receiving coil unit Lru1, the magnetic flux Bn1        which is widely circulated up to a place separated from the        power receiving coil unit Lru1 decreases. As a result, the        strength of an unnecessary leakage magnetic field which is        formed in a place separated from the power receiving coil unit        Lru1 is lowered. Furthermore, by the non-magnetic conductive        plate Sa which is disposed in an axis direction of the power        receiving coil Lr, magnetic coupling of the transmission coil Lt        or the power receiving coil Lr and the magnetic body Fa can be        prevented from excessively increasing, and thus magnetic        coupling of the transmission coil Lt and the power receiving        coil Lr can be prevented from significantly decreasing. As a        result, a decrease of power transmission efficiency is        suppressed.

In addition, in the power receiving coil unit Lru1 according to thepresent embodiment, when viewing from a facing direction of thetransmission coil Lt and the power receiving coil Lr, the outline of theconductive plate Sa is positioned in an outer side than the outline ofthe magnetic core Ct of the transmission coil Lt. Thus, the magneticcoupling of the transmission coil Lt and the magnetic body Fa iseffectively prevented from excessively increasing by the conductiveplate Sa. Also, among the magnetic fluxes which are generated by thetransmission coil Lt, the magnetic flux which is not interlinked withthe power receiving coil Lr selectively forms a magnetic path whichpasses though the magnetic body Fa. As a result, a decrease of powertransmission efficiency is suppressed, and an effect in which a leakagemagnetic field is reduced is increased even more.

Second Embodiment

Next, the wireless power transmission device S1 b according to a secondembodiment of the present invention will be described with reference toFIG. 3. FIG. 3 is a diagram schematically illustrating a magnetic fluxwhich is generated by first and second transmission coils, in across-sectional diagram illustrating a power receiving coil unitaccording to a second embodiment of the present invention, the first andsecond transmission coils, and a magnetic core of the first and secondtransmission coils. However, the figure schematically illustrates amagnetic flux which is generated by the first and second transmissioncoils Lta and Ltb, and does not illustrate magnetic fluxes in the insideof magnetic cores Ctb and Cr of the first and second transmission coilsLta and Ltb and the power receiving coil Lr, and the magnetic body Fa.In addition, in FIG. 3, as representations of the magnetic fluxes whichare generated by the first and second transmission coils Lta and Ltb, amagnetic flux Bt1 b which is interlinked with the power receiving coilLr, a magnetic flux Bn1 b which is widely circulated up to a placeseparated from the power receiving coil unit Lru1, and a magnetic fluxBf1 b which passes through the magnetic body Fa are illustrated.

A wireless power transmission device S1 b includes a wirelesstransmission device Ut1 b, and a wireless power receiving device Ur1 b.Furthermore, the wireless transmission device Ut1 b includes, the powersupply PW, the inverter INV, the first and second transmission coils Ltaand Ltb, and a magnetic core Ctb. In addition, the wireless powerreceiving device Ur1 b includes the power receiving coil unit Lru1, andthe rectification circuit DB.

Here, configurations of the power supply PW, the inverter INV, the powerreceiving coil unit Lru1, and the rectification circuit DB of thewireless power transmission device S1 b are the same as those of thewireless power transmission device S1 according to the first embodiment.The wireless power transmission device S1 b is different from thewireless power transmission device S1 in that the wireless powertransmission device S1 b includes the first and second transmissioncoils Lta and Ltb and the magnetic core Ctb, instead of the transmissioncoil Lt. Hereinafter, in the wireless power transmission device S1 b,different portions from the wireless power transmission device S1 willbe mainly described.

The first and second transmission coils Lta and Ltb are disposed on thesame plane, and the axis of the first and second transmission coils Ltaand Ltb are both parallel to a facing direction of the first and secondtransmission coils Lta and Ltb and the power receiving coil unit Lru1.The first and second transmission coils Lta and Ltb are respectivelyformed by winding the winding wire which is configured by a litz wire,such as, copper or aluminum, in a planar shape. The number of turns ofeach of the first and second transmission coils Lta and Ltb isapproximately set based on a predetermined distance between the powerreceiving coil unit Lru1 and the first and second transmission coils Ltaand Ltb, a desired power transmission efficiency, or the like. The firsttransmission coil Lta and the second transmission coil Ltb areelectrically connected in series to each other, and the first and secondtransmission coils Lta and Ltb are connected to the inverter INV. Thefirst and second transmission coils Lta and Ltb face the power receivingcoil Lru1, and thereby power is wirelessly transmitted.

In addition, the directions of the magnetic fields of the firsttransmission coil Lta and the second transmission coil Ltb when acurrent flows are reversed to each other. That is, in a case in whichthe first transmission coil Lta and the second transmission coil Ltbhave the same winding direction, the first and second transmission coilsLta and Ltb may be connected such that a direction of a current flowingthrough the first transmission coil Lta is reversed to a direction of acurrent flowing through the second transmission coil Ltb. Alternatively,in a case in which the first transmission coil Lta and the secondtransmission coil Ltb have reverse winding directions, the first andsecond transmission coils Lta and Ltb may be connected such that thedirection of the current flowing through the first transmission coil Ltais the same as the direction of the current flowing through the secondtransmission coil Ltb. By doing this, the directions of the magneticfields to be generated are reversed to each other, and thus a magneticpath which is interlinked with the transmission coils Lta and Ltb inboth directions is efficiently formed by the magnetic fields generatedin both coils.

The magnetic core Ctb is disposed along a side of the first and secondtransmission coils Lta and Ltb opposite to a side which faces the powerreceiving coil unit Lru1. The magnetic core Ctb is configured using amaterial with a relatively high relative permeability, such as aferrite. By the magnetic core Ctb, inductances of the first and secondtransmission coils Lta and Ltb are increased, and magnetic coupling ofthe first transmission coil Lta and the second transmission coil Ltb isincreased. Thus, an efficient magnetic flux can be generated.

In a case in which the center point of the magnetic core Ctb overlapsthe center point of the power receiving coil unit Lru1, when viewingfrom a facing direction of the first and second transmission coils Ltaand Ltb and the power receiving coil Lru1, the outline of the magneticcore Ctb is positioned in an inner side than the outline of theconductive plate Sa of the power receiving coil unit Lru1. That is, whenviewing from a facing direction of the first and second transmissioncoils Lta and Ltb and the power receiving coil Lru1, the outline of theconductive plate Sa of the power receiving coil unit Lru1 is positionedin an outer side than the outline of the magnetic core Ctb. For thisreason, the magnetic coupling of the first and second transmission coilsLta and Ltb and the magnetic body Fa is effectively prevented fromexcessively increasing by the conductive plate Sa. Also, among themagnetic fluxes which are generated by the first and second transmissioncoils Lta and Ltb, the magnetic flux which is not interlinked with thepower receiving coil Lr selectively forms a magnetic path which passesthough the magnetic body Fa. As a result, a decrease of powertransmission efficiency is suppressed, and an effect in which a leakagemagnetic field is reduced is increased even more.

Next, a magnetic flux which is generated by the first and secondtransmission coils Lta and Ltb and a reduction effect of an unnecessaryleakage magnetic field will be described in detail with reference toFIG. 3.

As illustrated in FIG. 3, the first and second transmission coils Ltaand Ltb generate the magnetic flux Bt1 b which is interlinked with thepower receiving coil Lr. Since the magnetic flux Bt1 b is interlinkedwith the power receiving coil Lr, an electromotive force is generated inthe power receiving coil Lr.

Meanwhile, as illustrated in FIG. 3, the first and second transmissioncoils Lta and Ltb generate the magnetic flux Bn1 b which is notinterlinked with the power receiving coil Lr and is widely circulated upto a place separated from the power receiving coil unit Lru1, and themagnetic flux Bf1 b which is not interlinked with the power receivingcoil Lr and passes through the magnetic body Fa. Here, since a magneticpath with a magnetoresistance lower than that of a surrounding space isformed by the magnetic body Fa with a higher permeability than that ofthe surrounding space, the magnetic flux Bn1 b which is widelycirculated up to a place separated from the power receiving coil unitLru1 is reduced, an unnecessary leakage magnetic field which is formedin a place separated from the power receiving coil unit Lru1 is reduced.

Here, in the power receiving coil unit Lru1, since the conductive plateSa is installed along a surface on a side of the power receiving coil Lropposite to a surface which faces the first and second transmissioncoils Lta and Ltb, the magnetic flux Bt1 b forms a magnetic path whichpasses through the magnetic body Fa, and thereby a decrease of themagnetic flux which is interlinked with the power receiving coil Lr issuppressed. That is, by the conductive plate Sa, magnetic coupling ofthe first and second transmission coils Lta and Ltb or the powerreceiving coil Lr, and the magnetic body Fa can be prevented fromexcessively increasing, and magnetic coupling of the first and secondtransmission coils Lta and Ltb and the power receiving coil Lr can beprevented from significantly decreasing. As a result, a decrease ofpower transmission efficiency is suppressed.

Particularly, in the present embodiment, when viewing from a facingdirection of the first and second transmission coils Lta and Ltb and thepower receiving coil unit Lru1, the outline of the conductive plate Sais positioned in an outer side than the outline of the magnetic core Ctbof the first and second transmission coils Lta and Ltb. Thus, by forminga magnetic path such that the magnetic flux Bt1 b passes through themagnetic body Fa, a decrease of a magnetic flux which is interlinkedwith the power receiving coil Lr can be effectively suppressed. That is,by the conductive plate Sa, the magnetic coupling of the first andsecond transmission coils Lta and Ltb and the magnetic body Fa iseffectively prevented from excessively increasing.

As described above, in the power receiving coil unit Lru1 according tothe present embodiment, when viewing from a facing direction of thefirst and second transmission coils Lta and Ltb and the power receivingcoil Lr, the outline of the conductive plate Sa is positioned in anouter side than the outline of the magnetic core Ctb of the first andsecond transmission coils Lta and Ltb. Thus, magnetic coupling of thefirst and second transmission coils Lta and Ltb and the magnetic body Fais prevented from excessively increasing by the conductive plate Sa.Also, among the magnetic fluxes which are generated by the first andsecond transmission coils Lta and Ltb, the magnetic flux which is notinterlinked with the power receiving coil Lr selectively forms amagnetic path which passes through the magnetic body Fa. As a result, adecrease of power transmission efficiency is suppressed, and an effectin which a leakage magnetic field is reduced is increased even more.

Third Embodiment

Next, a wireless power transmission device S2 according to a thirdembodiment of the present invention will be described with reference toFIG. 4. In the present embodiment, an example in which a coil unitaccording to the present invention is applied to a transmission coilunit of a wireless power transmission device will be described. FIG. 4is a diagram schematically illustrating magnetic fluxes which aregenerated by the transmission coil, in a cross-sectional diagramillustrating a transmission coil unit according to the third embodimentof the present invention and a power receiving coil. However, in thefigure, magnetic fluxes in the magnetic cores Ct and Cr of thetransmission coil Lt and a power receiving coil Lr, and a magnetic fluxin the magnetic body Fb are not illustrated. In addition, in FIG. 4, asrepresentations of the magnetic fluxes which are generated bytransmission coil Lt, a magnetic flux Bt2 which is interlinked with thepower receiving coil Lr, a magnetic flux Bn2 which is widely circulatedup to a place separated from the transmission coil unit Ltu1, and amagnetic flux Bf2 which passes through the magnetic body Fb areillustrated.

The wireless power transmission device S2 includes a wirelesstransmission device Ut2 and a wireless power receiving device Ur2. Thewireless transmission device Ut2 includes the power supply PW, theinverter INV, and the transmission coil unit Ltu1. The wireless powerreceiving device Ur2 includes the power receiving coil Lr and therectification circuit DB. Here, configurations of the power supply PW,the inverter INV, and the rectification circuit DB are the same as thoseof the wireless power transmission device S1 according to the firstembodiment. The wireless power transmission device S2 according to thethird embodiment of the present invention is different from the wirelesspower transmission device S1 according to the first embodiment in thatthe wireless power transmission device S2 includes the transmission coilunit Ltu1 instead of the transmission coil Lt, and includes the powerreceiving coil Lr instead of the power receiving coil unit Lru1. Aconfiguration of the power receiving coil Lr according to the presentembodiment is the same as the power receiving coil Lr included in thepower receiving coil unit Lru1 according to the first embodiment. Thatis, in the power receiving coil Lr according to the present embodiment,the conductive plate Sa and the magnetic body Fa are removed from thepower receiving coil unit Lru1 according to the first embodiment.Hereinafter, the portions different from those of the first embodimentwill be mainly described.

The configuration of the transmission coil unit Ltu1 will be firstdescribed. The transmission coil unit Ltu1 includes the transmissioncoil Lt, a conductive plate Sb, and a magnetic body Fb. Eachconfiguration of the transmission coil Lt, the conductive plate Sb, andthe magnetic body Fb is the same as each configuration of thetransmission coil Lt of the wireless transmission device Ut2 which isincluded in the wireless power transmission device S1 according to thefirst embodiment, the conductive plate Sa which is included in the powerreceiving coil unit Lru1 according to the first embodiment, and themagnetic body Fa.

The conductive plate Sb is disposed in an axis direction of thetransmission coil Lt. Specifically, the conductive plate Sb is disposedalong a surface on a side of the transmission coil Lt opposite to asurface which faces the power receiving coil Lr, when viewing from afacing direction of the transmission coil unit Ltu1 and the powerreceiving coil Lr, an outline of the conductive plate Sb is positionedin an outer side than an outline of the magnetic core Ct of thetransmission coil Lt. For this reason, magnetic coupling of thetransmission coil Lt and the magnetic body Fb is effectively preventedfrom excessively increasing by the conductive plate Sb. Also, among themagnetic fluxes which are generated by the transmission coil Lt, themagnetic flux which is not interlinked with the power receiving coil Lrselectively forms a magnetic path which passes though the magnetic bodyFb. As a result, a decrease of power transmission efficiency issuppressed, and an effect in which a leakage magnetic field is reducedis increased even more.

The magnetic body Fb is disposed along a surface of the conductive plateSb opposite to a surface which faces the transmission coil Lt. when thetransmission coil unit Ltu1 is viewed from the power receiving coil Lr,the magnetic body Fb protrudes toward outer both sides than the outlineof the conductive plate Sb in an axis direction of the transmission coilLt. In addition, since forming a magnetic circuit with a lowmagnetoresistance, the magnetic body Fb is configured by a material withrelatively high relative permeability, such as, steel or a ferrite. Inthe present embodiment, the magnetic body Fb is configured by one plate,but the invention is not limited to this. For example, multiple platesmay be disposed so as to be separated from each other. In all cases, amagnetic circuit with a high magnetoresistance can be formed by themagnetic body Fb.

In addition, the magnetic body Fb is positioned in an outer side than anoutline of one side of the conductive plate Sb in an axis direction ofthe transmission coil Lt. When viewing from an axis direction of thetransmission coil Lt, the magnetic body Fb includes a first portion F1Bwhich is positioned on a side of the conductive plate Sb opposite to aside which faces the transmission coil Lt. That is, the magnetic body Fbprotrudes toward an outer side (left side in the figure) than an outline(left end in the figure) of one side of the conductive plate Sb in anaxis direction of the transmission coil Lt.

In addition, furthermore, the magnetic body Fb is positioned in an outerside than an outline of the other side of the conductive plate Sb in anaxis direction of the transmission coil Lt. When viewing from an axisdirection of the transmission coil Lt, the magnetic body Fb includes asecond portion F2B which is positioned on a side of the conductive plateSb opposite to a side which faces the transmission coil Lt. That is, themagnetic body Fb protrudes toward an outer side (right side in thefigure) than an outline (right end in the figure) of the other side ofthe conductive plate Sb in an axis direction of the transmission coilLt. In a direction orthogonal to the axis direction of the transmissioncoil Lt, the magnetic body Fb may or may not protrude toward an outerside than the outline of the conductive plate Sb. In the presentembodiment, a length of the conductive plate Sb and a length of themagnetic body Fb are approximately the same, in a direction orthogonalto the axis direction of the transmission coil Lt.

Next, the magnetic flux which is generated by the transmission coil Ltaccording to the present embodiment, and a reduction effect of anunnecessary leakage magnetic field will be described in detail withreference to FIG. 4.

As illustrated in FIG. 4, the transmission coil Lt generates magneticfluxes Bt2 which are interlinked with the power receiving coil Lr. Sincethe magnetic fluxes Bt2 are interlinked with the power receiving coilLr, an electromotive force occurs in a winding wire Wr of the powerreceiving coil Lr. Then, the power generated by the power receiving coilLr is rectified by the rectification circuit DB, and is supplied to aload R. Here, since the conductive plate Sb is installed along a surfaceon a side of the transmission coil Lt opposite to a surface which facesthe power receiving coil Lr, the magnetic flux Bt2 forms a magnetic pathwhich passes through the magnetic body Fb, and thereby reduction of amagnetic flux which is interlinked with the power receiving coil Lr issuppressed. That is, by the conductive plate Sb, magnetic coupling ofthe transmission coil Lt and the magnetic body Fb can be prevented fromexcessively increasing, and magnetic coupling of the transmission coilLt and the power receiving coil Lr can be prevented from significantlydecreasing. As a result, a decrease of power transmission efficiency issuppressed. Particularly, in the present embodiment, when viewing from afacing direction of the transmission coil Lt and the power receivingcoil Lr, the outline of the conductive plate Sb is positioned in anouter side than the outline of the magnetic core Ct of the transmissioncoil Lt. Thus, by forming a magnetic path such that the magnetic fluxBt2 passes through the magnetic body Fb, a decrease of a magnetic fluxwhich is interlinked with the power receiving coil Lr can be effectivelysuppressed. That is, by the conductive plate Sb, the magnetic couplingof the transmission coil Lt and the magnetic body Fb is excessivelyprevented from excessively increasing.

Meanwhile, as illustrated in FIG. 4, the transmission coil Lt generatesthe magnetic flux Bn2 which is not interlinked with the power receivingcoil Lr, and is widely circulated up to a place separated from thetransmission coil unit Ltu1. The magnetic flux Bn2 which is widelycirculated up to a place separated from the transmission coil unit Ltu1forms an unnecessary leakage magnetic field in a place separated fromthe transmission coil unit Ltu1. In addition, the transmission coil Ltgenerates the magnetic flux Bf2 which is not interlinked with the powerreceiving coil Lr, and passes through the magnetic body Fb. Sincecirculating the periphery of the transmission coil unit Ltu1, themagnetic flux Bf2 which passes through the magnetic body Fb does notform a magnetic path which is circulated up to place separated from thetransmission coil unit Ltu1.

Here, in the transmission coil unit Ltu1, a magnetic path having amagnetoresistance lower than that of the surrounding space is formed bythe magnetic body Fb having permeability higher than that of asurrounding space, and thus, it is possible to reduce the magnetic fluxBn2 which widely circulates up to a place separated from thetransmission coil unit Ltu1, and to reduce an unnecessary leakagemagnetic field which is formed in a place separated from thetransmission coil unit Ltu1. Furthermore, the first and second portionsF1B and F2B of the magnetic body Fb is disposed so as to be positionedon the outside of both end of the conductive plate Sb, in an axisdirection of the transmission coil Lt, and thus, a magnetoresistance ofa magnetic path which is formed by the magnetic body Fb is furtherdecreased, and it is possible to effectively reduce an unnecessaryleakage magnetic field.

In addition, in the present embodiment, when the conductive plate Sb andthe transmission coil Lt are viewed from a facing direction of thetransmission coil Lt and the power receiving coil Lr, the outline of theconductive plate Sb is positioned in an outer side than the outline ofthe magnetic core Ct of the transmission coil Lt. Thus, it is possibleto more effectively suppress that the magnetic flux Bt2 which isinterlinked with the power receiving coil Lr forms a magnetic path whichpasses though the magnetic body Fb, and the magnetic flux which is notinterlinked with the power receiving coil Lr selectively forms amagnetic path which passes though the magnetic body Fb. As a result, adecrease of power transmission efficiency is suppressed, and an effectin which a leakage magnetic field is reduced is increased even more.

As described above, in the transmission coil unit Ltul according to thepresent embodiment, the magnetic body Fb includes the first portion F1Bwhich is positioned in an outer side than the outline of one side of theconductive plate Sb in an axis direction of the transmission coil Lt,and the second portion F2B which is positioned in an outer side than theoutline of the other side of the conductive plate Sb in an axisdirection of the transmission coil Lt, and thereby a magnetic path witha low magnetoresistance is formed. That is, since the magnetoresistanceof the magnetic path which passes through the magnetic body Fb issmaller than the magnetoresistance of the magnetic path which is widelycirculated up to a place separated from the transmission coil unit Ltu1,the magnetic flux Bn2 which is widely circulated up to a place separatedfrom the transmission coil unit Ltu1 decreases. As a result, thestrength of an unnecessary leakage magnetic field which is formed in aplace separated from the transmission coil unit Ltu1 is lowered.Furthermore, by the non-magnetic conductive plate Sb which is disposedin an axis direction of the transmission coil Lt, magnetic coupling ofthe transmission coil Lt and the magnetic body Fb is prevented fromexcessively increasing, and thus magnetic coupling of the transmissioncoil Lt and the power receiving coil Lr can be prevented fromsignificantly decreasing. As a result, a decrease of power transmissionefficiency is suppressed.

In addition, in the power receiving coil unit Ltu1 according to thepresent embodiment, when viewing from a facing direction of thetransmission coil Lt and the power receiving coil Lr, the outline of theconductive plate Sb is positioned in an outer side than the outline ofthe magnetic core Ct of the transmission coil Lt. Thus, the magneticcoupling of the transmission coil Lt and the magnetic body Fb iseffectively prevented from excessively increasing by the conductiveplate Sb. Also, among the magnetic fluxes which are generated by thetransmission coil Lt, the magnetic flux which is not interlinked withthe power receiving coil Lr that will be described later selectivelyforms a magnetic path which passes though the magnetic body Fb. As aresult, a decrease of power transmission efficiency is suppressed, andan effect in which a leakage magnetic field is reduced is increased evenmore.

Fourth Embodiment

Next, a wireless power transmission device S3 according to a fourthembodiment will be described with reference to FIG. 5 and FIG. 6. In thepresent embodiment, an example in which a coil unit according to thepresent invention is applied to a power receiving coil unit of awireless power transmission device will be described. FIG. 5 is adiagram schematically illustrating a magnetic flux is generated by atransmission coil, in a cross-sectional diagram illustrating a powerreceiving coil unit according to a fourth embodiment of the presentinvention and a transmission coil. FIG. 6 is a diagram schematicallyillustrating magnetic fluxes which are generated by the transmissioncoil, in a case in which a positional shift occurs in the powerreceiving coil unit and the transmission coil, in FIG. 5. In FIG. 5 andFIG. 6, magnetic fluxes in the inside of magnetic cores Ct and Cr andmagnetic body Fc of the transmission coil Lt and the power receivingcoil Lr are not illustrated. In addition, in FIG. 5, as representationsof the magnetic fluxes which are generated by the transmission coil Lt,a magnetic flux Bt3 which is interlinked with power receiving coil Lr, amagnetic flux Bn3 which is widely circulated up to a place separatedfrom the power receiving coil unit Lru2, and a magnetic flux Bf3 whichpasses through the magnetic body Fc are illustrated.

The wireless power transmission device S3 includes the wirelesstransmission device Ut1 and a wireless power receiving device Ur3.Furthermore, the wireless power receiving device Ur3 includes the powerreceiving coil unit Lru2 and the rectification circuit DB. Here,configurations of the wireless transmission device Ut1 and therectification circuit DB are the same as those of the wireless powertransmission device S1 according to the first embodiment. The wirelesspower receiving device Ur3 of the wireless power transmission device S3according to the fourth embodiment, is different from that of the firstembodiment in that the power receiving coil unit Lru2 is included thewireless power receiving device UR3 instead of the power receiving coilunit Lru1. Hereinafter, in the coil unit according to the fourthembodiment of the present invention, portions different from those ofthe first embodiment will be mainly described.

A configuration of the power receiving coil unit Lru2 will be firstdescribed with reference to FIG. 5. The power receiving coil unit Lru2includes the power receiving coil Lr, the conductive plate Sa, and themagnetic body Fc. Here, configurations of the power receiving coil Lr,and the conductive plate Sa are the same as those of the power receivingcoil Lr included in the power receiving coil unit Lru1 according to thefirst embodiment, and the conductive plate Sa. The power receiving coilunit Lru2 according to the present embodiment is different from thepower receiving coil unit Lru1 according to the first embodiment in thatthe magnetic body Fc is included in the power receiving coil unit Lru2instead of the magnetic body Fa.

The magnetic body Fc includes a first portion F1C, a second portion F2C,and a third portion F3C. When viewing from an axis direction of thepower receiving coil Lr, the first portion F1C is disposed so as to bepositioned on a surface of the conductive plate Sa opposite to a surfacewhich faces the power receiving coil Lr. In addition, the first portionF1C is disposed so as to be positioned in an outer side than an outlineof one side of the conductive plate Sa in an axis direction of the powerreceiving coil Lr. The first portion F1C is configured also by amaterial such as a ferrite with a relatively low imaginary componentvalue of permeability, among magnetic bodies with high permeability.

When viewing from an axis direction of the power receiving coil Lr, thesecond portion F2C is disposed so as to be positioned on a surface sideof the conductive plate Sa opposite to a surface which faces the powerreceiving coil Lr. In addition, the second portion F2C is disposed so asto be positioned in an outer side than an outline of the other side ofthe conductive plate Sa in an axis direction of the power receiving coilLr. The second portion F2C is configured also by a material such as aferrite with a relatively low imaginary component value of permeability,among magnetic bodies with high permeability.

The third portion F3C is disposed along a surface of the conductiveplate Sa opposite to a surface which faces the power receiving coil Lr.In addition, in the present embodiment, an end (left end of the figure)of one side of the third portion F3C in an axis direction of the powerreceiving coil Lr, is connected to the first portion F1C, and an end(right end of the figure) of the other side of the third portion F3C isconnected to the second portion F2C. That is, the first and secondportions F1C and F2C are connected to each other through the thirdportion F3C. In this case, a magnetoresistance of a magnetic path whichis formed by a magnetic flux which passes through the magnetic body Fcis further lowered, and thus it is possible to more reliably increase areduction effect of a leakage magnetic field. The third portion F3C isconfigured by a material such as steel with a relatively high relativepermeability.

Here, even if the third portion F3C is configured by a material such asa ferrite with a relatively low imaginary component value ofpermeability in the same manner as in the first and second portions F1Cand F2C, it is possible to obtain a reduction effect of a leakagemagnetic field. However, as illustrated in FIG. 5, since the thirdportion F3C has a shape which is longer than the power receiving coilLr, and is a little thin, in a case in which the power receiving coilunit Lru2 according to the present embodiment is mounted in a movingbody such as a lower portion of a vehicle, if the third portion F3C isconfigured by a ferrite, there is a possibility that a mechanicalstrength of the third portion F3C may not withstand the vibration of themoving body. Thus, it is preferable that the third portion F3C isconfigured by a magnetic body with a relatively high mechanicalstrength.

Next, a magnetic flux which is generated by the transmission coil Ltaccording to the present embodiment, and a reduction effect of anunnecessary leakage magnetic field will be described in detail withreference to FIG. 5.

As illustrated in FIG. 5, the transmission coil Lt generates themagnetic flux Bt3 which is interlinked with the power receiving coil Lr.Since the magnetic flux Bt3 is interlinked with the power receiving coilLr, a electromotive force occurs in a winding wire Wr of the powerreceiving coil Lr. Here, since the conductive plate Sa is installedalong a side opposite to a power receiving side of the power receivingcoil Lr, magnetic coupling of the transmission coil Lt or the powerreceiving coil Lr, and the magnetic body Fc can be prevented fromexcessively increasing, and magnetic coupling of the transmission coilLt and the power receiving coil Lr can be prevented from significantlydecreasing.

Meanwhile, as illustrated in FIG. 5, the transmission coil Lt generatesthe magnetic flux Bn3 which is not interlinked with the power receivingcoil Lr and is widely circulated up to a place separated from the powerreceiving coil unit Lru2, and the magnetic flux Bf3 which is notinterlinked with the power receiving coil Lr and passes through themagnetic body Fc. Here, since a magnetic path with a magnetoresistancelower than that of a surrounding space is formed by the magnetic body Fcwith a higher permeability than that of the surrounding space, themagnetic flux Bn3 which is widely circulated up to a place separatedfrom the power receiving coil unit Lru2 can be reduced, and anunnecessary leakage magnetic field which is formed in a place separatedfrom the power receiving coil unit Lru2 can be reduced.

Next, with reference to FIG. 6, a case in which a positional shiftoccurs in the transmission coil Lt and the power receiving coil unitLru2 will be described. FIG. 6 illustrates a case in which a position ofthe power receiving coil unit Lru2 is shifted with respect to thetransmission coil Lt, and the first portion F1C of the magnetic body Fcapproaches an end of the transmission coil Lt.

As illustrated in FIG. 6, when the first portion F1C of the magneticbody Fc approaches the end of the transmission coil Lt, a magnetic fluxwhich passes through the first portion F1C significantly increases. Thatis, magnetic flux density of the first portion F1C is locally increased.In this way, if magnetic flux density of a magnetic body is increased,there is a possibility that loss and heat generation may besignificantly increased. In contrast to this, in the present embodiment,the first portion F1C is configured by a material such as a ferrite witha relatively low imaginary component value of permeability, and therebyeven if the magnetic flux density of the first portion F1C is increased,it is possible to reduce a significant loss and heat generation. Inaddition, even in a case in which the power receiving coil unit Lru2 isshifted in a reverse direction to the direction illustrated in FIG. 6,and the second portion F2C of the magnetic body Fc approaches an end ofthe transmission coil Lt, the second portion F2C is configured by amaterial such as a ferrite with a relatively low imaginary componentvalue of permeability, in the same manner as above. Thus, even ifmagnetic flux density of the second portion F2C is increased, it ispossible to reduce a significant loss and heat generation.

As described above, in the power receiving coil unit Lru2 according tothe present embodiment, the magnetic body Fc includes a first portionF1C which is positioned in an outer side than the outline of one side ofthe conductive plate Sa in an axis direction of the power receiving coilLr, and the second portion F2C which is positioned in an outer side thanthe outline of the other side of the conductive plate Sa in an axisdirection of the power receiving coil Lr, and thereby a magnetic pathwith a low magnetoresistance is formed. That is, since themagnetoresistance of the magnetic path which passes through the magneticbody Fc is smaller than the magnetoresistance of the magnetic path whichis widely circulated up to a place separated from the power receivingcoil unit Lru2, the magnetic flux Bn3 which is widely circulated up to aplace separated from the power receiving coil unit Lru2 decreases. As aresult, the strength of an unnecessary leakage magnetic field which isformed in a place separated from the power receiving coil unit Lru2 islowered. Furthermore, by the non-magnetic conductive plate Sa which isdisposed in an axis direction of the power receiving coil Lr, magneticcoupling of the transmission coil Lt or the power receiving coil Lr andthe magnetic body Fc can be prevented from excessively increasing, andthus magnetic coupling of the transmission coil Lt and the powerreceiving coil Lr can be prevented from significantly decreasing. As aresult, a decrease of power transmission efficiency is suppressed.

Furthermore, the power receiving coil unit Lru2 according to the presentembodiment, imaginary component values of permeability of the first andsecond portions F1C and F2C of the magnetic body Fc are smaller than animaginary component value of permeability of the third portion F3C.Thus, even if the position of the power receiving coil unit Lru2 isshifted, when the first and second portions F1C and F2C which ispositioned in an outer side than the outline of the conductive plate Saapproaches the transmission coil Lt which face the power receiving coilunit Lru2, the loss and heat generation of the first and second portionsF1C and F2C can be reduced, even if the magnetic flux density of thefirst and second portions F1C and F2C is locally increased.

Hereinafter, a specific description on a decrease of the unnecessaryleakage magnetic field and suppressing of the decrease of powertransmission efficiency according to the above-described embodimentswill be made using first and second examples and a comparative example.

As the first example, the wireless power transmission device S1according to the first embodiment has been used. As the second example,the wireless power transmission device S3 according to the fourthembodiment described above was. In addition, in order to comparecharacteristics of a comparative example with those of the first andsecond examples, a wireless power transmission device in which theconductive plate Sa and the first and second magnetic body Fa wereremoved has been used in the wireless power transmission device S1according to the first embodiment.

A configuration of a transmission coil Lt10 and a power receiving coilLr10 of a wireless power transmission device of the comparative examplewill be first described with reference to FIG. 7. FIG. 7 is across-sectional diagram illustrating a power receiving coil and atransmission coil of the comparative example. The transmission coil Lt10is a solenoid coil in which a magnetic core Ct10 is wound by a windingwire Wt10 in a helical shape, and a power receiving coil Lr10 is asolenoid coil in which a magnetic core Cr10 is wound by a winding wireWr10. That is, in the wireless power transmission device of thecomparative example, the conductive plate Sa and the magnetic body Faare removed from the wireless power transmission device S1 according tothe first embodiment.

Here, in the first and second examples and the comparative example, alitz wire that is obtained by twisting approximately 4000 copper wireswhich are coated with polyimide and which respectively have a diameterof 0.05 mm, and that has a diameter of approximately 6 mm has been usedfor winding wires Wt and Wt10 of the transmission coils Lt and Lt10 andfor winding wires Wr and Wr10 of the power receiving coils Lr and Lr10.In addition, a ferrite (with relative permeability of approximately3000) with a length 300 mm, a width of 300 mm, and a thickness of 30 mmhas been used for the magnetic cores Ct and Ct10 of the transmissioncoils Lt and Lt10, and the magnetic cores Cr and Cr10 of the powerreceiving coils Lr and Lr10. The transmission coils Lt and Lt10 and thepower receiving coils Lr and Lr10 are respectively configured by windingthe winding wires Wt, Wt10, Wr, and Wr10 by 30 turns in a helical shape.

In addition, in the power receiving coil units Lru1 and Lry2 of thefirst and second examples, an aluminum plate with a length of 600 mm, awidth of 500 mm, and a thickness of 3 mm has been used as the conductiveplates Sa and Sb, and in the power receiving coil unit Lru1 of the firstexample, a plate with a length of 600 mm, a width of 500 mm, and athickness of 3 mm, in which magnetic body powder was solidified withresin, has been used as the magnetic body Fa. A magnetic body F wasdisposed so as to protrude by 50 mm on both outsides in an axisdirection of the power receiving coil Lr of the conductive plate Sa.Meanwhile, in the power receiving coil unit Lru2 of the second example,a ferrite (loss is equal to or less than 350 kW/m³, in 100 kHz and 200mT) which has a length of 50 mm, a width of 50 mm, and a thickness of 40mm and in which an imaginary component value of permeability isrelatively small and loss is less, has been used as the first and secondportions F1C and F2C of the magnetic body Fc, and a steel plate with alength of 100 mm, a width of 500 mm, and a thickness of 3 mm has beenused as the third portion F3C.

Subsequently, in the first and second examples and the comparativeexample, power transmission efficiency and an unnecessary leakagemagnetic field have been measured. At this time, in a state in which adistance between the transmission coils Lt and Lt10 and the powerreceiving coils Lr and Lr10 has been set to 100 mm, the transmissioncoils Lt and Lt10 and the power receiving coils Lr and Lr10 have beendisposed such that the centers of the transmission coils Lt and Lt10 andthe centers of the power receiving coils Lr and Lr10 are identical toeach other, when viewing from a facing direction of the transmissioncoils Lt and Lt10 and the power receiving coils Lr and Lr10. Inaddition, in order to adjust an impedance of an electrical circuit,capacitors with capacitances according to impedances of the transmissioncoils Lt and Lt10 or the power receiving coils Lr and Lr10 have beeninserted in series to the transmission coils Lt and Lt10, and the powerreceiving coils Lr and Lr10, and the measurement has been performed. Asupplying power of the power supply PW was adjusted such that the powerwhich is supplied to the load R is 1.5 kW.

As the power transmission efficiency, while taking into account loss ofthe inverter INV and loss of the rectification circuit DB which wasmeasured in ad advance, an efficiency between the transmission coil unitand the power receiving coil has been calculated, based on the measuredresult of the power which is supplied by the power supply PW and thepower which is supplied to the load R.

For an unnecessary leakage magnetic field, a magnetic field strength ona position separated from the centers of the power receiving coils Lrand Lr10 by 10 m has been used as an indicator. In a state in which aloop antenna was installed in a position separated by 10 m in an axisdirection of the power receiving coils Lr and Lr10 from the center ofthe power receiving coils Lr and Lr10, the magnetic field strength hasbeen measured. Here, in the loop antenna, magnetic field strengths inthree orthogonal directions (X, Y, Z directions) have been measured, andby synthesizing the magnetic field strengths, the leakage magnetic fieldhas been calculated. The transmission coils Lt and Lt10 have beeninstalled in a position with a height of 500 mm from a floor surface,such that a surface through power is transmitted faces the top. Thepower receiving coils Lr and Lr10 have been installed above thetransmission coils Lt and Lt10, so as to be disposed at an interval of100 mm. In addition, the loop antenna was installed such that its centeris positioned in a height of 1.5 m from the floor of a radio anechoicchamber.

The measured results of the first and second examples and thecomparative example are illustrated in FIG. 8. In the figure, a bargraph indicates a leakage magnetic field strength, and a line graphindicates power transmission efficiency.

To begin with, if the measured results of the first and second examplesare compared to each other, both the power transmission efficiency andthe leakage magnetic field strength are approximately the same. Next, ifthe measured results of the first and second examples are compared tothe measured result of the comparative example, the power transmissionefficiency in the first and second examples is approximately the same asthe power transmission efficiency in the comparative example. Incontrast to this, the leakage magnetic field strength in the first andsecond examples is significantly lower than the leakage magnetic fieldstrength in the comparative example. That is, in the first and secondexamples, it can be seen that the leakage magnetic field strength isreduced without decreasing the power transmission efficiency. Asdescribed above, it is confirmed that the power receiving coil unitsLru1 and Lru2 in the first and second examples can reduce an unnecessaryleakage magnetic field which is formed in a separated place, without adecrease of the power transmission efficiency.

As described above, the preset invention is described based on theembodiments. It is understood by those skilled in the art that theembodiments are exemplifications, various modifications and changes arepossible within the scope of the present invention, and suchmodifications and changes are included in the scope of the presentinvention. Thus, the description and drawings in the specification arenot limitative, and must be illustratively treated.

1. A coil unit which wirelessly transmits power from a transmission sideto a power receiving side, comprising: a coil on which a winding wire iswound in a helical shape; a non-magnetic conductive plate which isdisposed along an axis of the coil; and a magnetic body, wherein themagnetic body includes a first portion which is positioned in an outerside than an outline of one side of the conductive plate in an axisdirection of the coil, and a second portion which is positioned in anouter side than an outline of the other side of the conductive plate inthe axis direction of the coil, and wherein when viewing from the axisdirection of the coil, the first and second portions are positioned on aside of the conductive plate where is opposite to a side which faces thecoil.
 2. The coil unit according to claim 1, wherein the magnetic bodyfurther includes a third portion which is positioned between the firstportion and the second portion, and wherein imaginary component valuesof permeability of the first and second portions are smaller than animaginary component value of permeability of the third portion.
 3. Awireless power transmission device which wirelessly transmits power by atransmission coil and a power receiving coil unit facing each other,comprising: the transmission coil in which a winding wire is wound on amagnetic core; and the power receiving coil unit which is configuredwith the coil unit according to claim 1, wherein when viewing from afacing direction of the transmission coil and the power receiving coilunit, an outline of the conductive plate of the power receiving coilunit is positioned in an outer side than an outline of the magneticcore.
 4. A wireless power transmission device which wirelessly transmitspower by first and second transmission coils and a power receiving coilunit facing each other, comprising: the first and second transmissioncoils in which directions of magnetic fields generated when a currentflows are reversed to each other, and are apposed; a magnetic core whichis disposed along an arrangement direction of the first and secondtransmission coils; and the power receiving coil unit which isconfigured with the coil unit according to claim 1, wherein when viewingfrom a facing direction of the first and second transmission coils andthe power receiving coil unit, an outline of the conductive plate of thepower receiving coil unit is positioned in an outer side than an outlineof the magnetic core.
 5. A wireless power transmission device whichwirelessly transmits power by a transmission coil unit and a powerreceiving coil facing each other, comprising: the transmission coil unitwhich is configured with the coil unit according to claim 1; and thepower receiving coil, wherein the coil of the transmission coil unitincludes a magnetic core, and wherein when viewing from a facingdirection of the transmission coil unit and the power receiving coil, anoutline of the conductive plate of the transmission coil unit ispositioned in an outer side than an outline of the magnetic core.
 6. Awireless power transmission device which wirelessly transmits power by atransmission coil and a power receiving coil unit facing each other,comprising: the transmission coil in which a winding wire is wound on amagnetic core; and the power receiving coil unit which is configuredwith the coil unit according claim 2, wherein when viewing from a facingdirection of the transmission coil and the power receiving coil unit, anoutline of the conductive plate of the power receiving coil unit ispositioned in an outer side than an outline of the magnetic core.
 7. Awireless power transmission device which wirelessly transmits power byfirst and second transmission coils and a power receiving coil unitfacing each other, comprising: the first and second transmission coilsin which directions of magnetic fields generated when a current flowsare reversed to each other, and are apposed; a magnetic core which isdisposed along an arrangement direction of the first and secondtransmission coils; and the power receiving coil unit which isconfigured with the coil unit according claim 2, wherein when viewingfrom a facing direction of the first and second transmission coils andthe power receiving coil unit, an outline of the conductive plate of thepower receiving coil unit is positioned in an outer side than an outlineof the magnetic core.
 8. A wireless power transmission device whichwirelessly transmits power by a transmission coil unit and a powerreceiving coil facing each other, comprising: the transmission coil unitwhich is configured with the coil unit according to claim 2; and thepower receiving coil, wherein the coil of the transmission coil unitincludes a magnetic core, and wherein when viewing from a facingdirection of the transmission coil unit and the power receiving coil, anoutline of the conductive plate of the transmission coil unit ispositioned in an outer side than an outline of the magnetic core.